Can a rural hukou without a unit buy social security? I want to buy only old-age insurance, where and how to do it.

At present, rural hukou can also apply for social endowment insurance, which can be handled at the local labor insurance office according to flexible employment (requiring the letter of proof from landless farmers) or individual industrial and commercial households (providing relevant materials for engaging in individual business). In addition, the state is prepared to carry out rural insurance. As for the endowment insurance of insurance companies, it has a certain commercial nature, which is different from social security.

Further reading: How to buy insurance, which is good, and teach you how to avoid these "pits" of insurance.